I would like to know which is the best way to manatain a calc for a long time (more than 20 years).It mus be with or wihtout batteries, I know that you have the response, what about the keyboard , the LCD?
Lots of questions....
Thanks.

I think that you must store it in a box with 'silica-gel' bags to avoid de moisture, and isolated from great temperature variations (a box with styrofoam carved to hold the calc). I *think* that is a good idea, I don't tryed myself... And maybe a duplicate to assure the long-life?

The primary component failure that limits the life of a lot of electronics are capacitors that have a finite lifespan. So even if the silicon parts are OK, be prepared to replace the capacitors at some point....

From experience, actually happening in the last few months (after about 10 years).
The first failure is the [ON] key which from what I read is due to some foam padding losing its elasticity and not depressing the contacts for the keyboard. I don't know how to prevent this (maybe humidity) nor to cure it without openning (and maybe killing) the calc.

Some have mentioned the need to turn on a calculator from time to time, to keep the electrolytic capacitors in working order. Would be nice to learn the specifics of how this works. Does the electrolyte degrade in time with absence of charge?

I know I read somewhere, I think it was Randy Sloyer that said the LCD's of the Pioneer series has a definite lifetime. And won't last forever. I collect only the pioneer series,48 series and the 41CX, but I really won't like after 15 years they can't turn on because of an LCD problem. Any advice, or would they last a lifetime [25-30 years God willing ]

Electrolytic capacitors degrade over time if they are not used. They can be "reformed" by gradually applying a voltage. An old trick for restoring equipment that had sat on the shelf for too long, was to plug it into a variac and slowly increase the voltage from 0 to the nominal line voltage. This allowed the capacitors to reform without blowing them up by immediately applying full voltage.

Corrosion can be a problem for mechanical contacts if no voltage is present on the junction. The telephone company uses something called "sealing current" on subscriber loops to prevent corrosion at points where wires are spliced together.

1) Leave batteries in it and have them leak. If it is in the normal operating position, its cosmetic damage only that can be cleaned up as it just leaks on to the battery clips and cover. If it is keyboard down, the electrolyte gets into the keyboard - end of calculator.

2) Heavy use in dirty environments. Survey use without a cover claims most of the 48's. Fine dirt works it way into the keyboard and compromises individual key switches. You end up with intermittent keys. Concrete plants are particularly nasty. Again, no solution.

The whole electrolytic capacitor debate does not apply to HP calculators. A lot of this is technical urban legend stuff - comes from old time tube equipment that runs at 150 volts and above for the plate supplies. The filter caps dry out with time (we're talking 30 years and older here) and when hit with these high voltage levels, they tend to arc internally and short. Best to replace them, period. The variac method does help for really old equipment that you would want to keep working with 100% original parts. Otherwise, it's always best to replace them.

There is only one electrolytic cap in a 48 - a 1000uf 6 volt memory backup/battery bypass cap. Everything else is a sealed tantalum. Good for just about forever. Modern 6 volt electrolytics with pure DC applied from batteries will last just about as long if not overheated.

With Pioneers and 48's, I would say chalk is not as bad as dirt or concrete dust, but dirt in general is not good. Just turn them over and shake them out as I think blowing them out with canned air might help to drive the dirt inside. Just a thought, no data to back that up.

Voyagers and 41's are better sealed in the keyboard department and the metal discs used are less prone to wear. The Pioneers and 48's use a printed conductive ink thousands of times thinner and therefore wears much faster.

Hmmm, I suppose some of my $7 cheapies weren't all that low quality; it might have been the environment they operated in! I guess, a dry paper towel wipe maybe followed by a slightly damp one would be enough to get chalk dust off.

But as for concrete dust, I think your idea is best. I'd would then just turn the calc upside down, tap and shake gently. Boy I wonder what an industrial grade cased calculator would cost!

Speaking as an electronics reliability engineer (Yes, I am doing rocket science, Ha!) I would say this about electrolytic capacitors:

Aluminum electrolytics should have a voltage applied, say once a month, to keep the dielectric well formed. They also have the problem of drying out. Not too much you can do about that.

Dry tantalum electrolytics stored under good shelf conditions do not have either of the above two problems.

Wet tantalums are sufficiently well sealed to avoid the problem of drying out.

The real question is, "What sort of capacitors are to be found in HP calculators?" Here Randy Sloyer can probably offer a better opnion than mine, but if I had to guess I would say tantalums. If there is a 1000 µf 6 v capacitor it is probably a wet one.

Incorrect for absolutely longest term storage life, but I leave mine powered up in the drawer and check the batteries for power level and corrosion once a month. A weak point here is that I have seen both alkaline and Ni-Cad batteries leak while they still had a good charge on them. But they usually grow a little white fuzz on the end before they start turning the battery compartment contacts green. 98 times out of a hundred they run down bfore leaking.

In one of my super high reliability projects we use a very large wet tantalum capacitor rather than a battery to hold up mermory for some time in the event of a power interruption. Batteries are viewed with a jaundiced eye for this sort of application.